Expose session name in status line JSON data

Feature Request

When using a custom status line script (via settings.json → status_line), the JSON data piped to the script includes session_id but does not include the session name set via /rename.

Use Case

I manage many Claude Code sessions across different project directories and use /rename to give them meaningful names. I'd like to display the session name in my status line so I can always see which session I'm in at a glance — especially useful when switching between sessions with /resume.

Current Behavior

The status line JSON includes:

• session_id (raw UUID)
• No session name field

Requested Behavior

Add a session_name field (or similar) to the status line JSON that contains the name set via /rename. If no name has been set, it could be null or fall back to the session_id.

Example

{
  "session_id": "abc123-...",
  "session_name": "synapse-auth-flow",
  ...
}

This would allow status line scripts to display the human-readable session name instead of (or alongside) the raw ID.